This project addresses the hypothesis that we can retarget potent anti-viral immune responses to also become potent anti-tumor immune responses by genetically engineering antiviral T cells to over express T cell receptors (TCR) specific for tumor associated antigens. We propose to specifically engineer cytomegalovirus (CMV) pp65(495-503) peptide specific T cells to also recognize the E75 T cell epitope of the tumor antigen HER2/neu. We have found that high levels of CMV specific T cells are present in CMV seropositive patients and know that recovery of circulating CMV specific T cells provides protection against CMV disease. Although passive administration of HER2/neu specific antibodies have clinical effects on HER21neu specific tumors, attempts to immunize patients against HER2/neu to achieve high levels of circulating anti-HER2/neu specific T cells have had limited success. We have demonstrated the feasibility of cloning T cell receptors to melanoma antigens into human T cells, demonstrating our ability to retarget the antigen specificity of human T cells. Therefore, we propose to produce dual specificity T cells by over expressing a high affinity T cell receptor specific for HER2/neu E75 in T cells with existing antigen specificity against CMV pp65 (495-503) peptide. This application proposes to support the pre-clinical studies to test this hypothesis. The construction of the reagents proposed in this application will allow us to test fundamental questions about TCR affinity and avidity by comparing high and low affinity TCR in these dual specificity T cells. These studies will lead to a better understanding about the role of antigen specific T cells in eradicating CMV and HER2/neu expressing cells in breast cancer patients.They will also provide the preclinical data for a subsequent clinical trial to address a fundamental question in clinical cancer immunotherapy: "In the presence of a highly effective cellular response, defined as being of a magnitude sufficient to eradicate CMV expressing cells, will a HER2/neu directed immune response mediated by the same T cells be sufficient to delay recurrence of HER2/neu expressing tumor"?